The present invention relates to a method of controlling and/or regulating the slip of a clutch, for example, a clutch of a transmission, for example, of a CVT transmission having a driving element and an output element, measured driving rotational speeds and measured output rotational speeds being used to control and/or regulate the slip. In addition, the present invention relates to a device for controlling and/or regulating the slip of a clutch, for example, a clutch of a transmission, for example, of a CVT transmission, having a driving element and an output element, the device using measured driving rotational speeds and measured output rotational speeds to control and/or regulate the slip of the clutch.
Control and/or regulation of the slip of a clutch is understood to refer to control and/or regulation of the input rotational speed, i.e., the driving rotational speed and the output rotational speed, i.e., the driven rotational speed, so that a permanent deviation between the rotational speeds (equals slip) exists. Such a control and/or regulation of the slip of a clutch may be used with various types of clutches, such as torque converter lockup clutches, forward clutches and/or reverse clutches. When used with motor vehicles, the control and/or regulation of the slip of the clutch results in improvements in comfort and/or consumption, depending on the application. In addition, sudden changes in torque may be prevented by controlling and/or regulating the slip of the clutch.
CVT transmissions are continuously variable transmissions. Such transmissions may include, for example, two bevel gear pairs and a belt part (e.g., a steel thrust belt). One of the bevel gear pairs is connected to a drive, e.g., an internal combustion engine, while the other bevel gear pair is connected to an output. To adjust the gear ratio of the CVT transmission and the tension of the belt part, the driving bevel gear pair (i.e., the driving disk or primary disk) and the output bevel gear pair (i.e., the output disk or the secondary disk) each may include one axially stationary bevel gear and one axially movable bevel gear. In general, the axially movable bevel gears are pressed against the belt part by generating a hydraulic pressure, e.g., by a pump. The desired gear ratio of the CVT transmission and the required tension of the belt part may be adjusted through a suitable choice of the contact pressures. The pump for the hydraulic drive of the bevel gears may be driven by the combustion engine, for example. A torque converter and a planetary gear set having clutches for driving both forward and in reverse may be provided for the power transmission from the engine to the driving bevel gear pair. If the belt part twists or slips between the two bevel gear pairs, problems may occur, such as severe damage to or total destruction of the transmission, for example, by torque surges. To eliminate this problem, a clutch, for example, a slipping forward clutch, may be provided, for example, on the output side of the CVT transmission, i.e., between the output bevel gear pair and a driven axle. This may allow torque surges originating from a poor road surface to be attenuated. Thus, the belt part (e.g., a steel thrust belt), which may be destroyed by unattenuated torque surges, may be protected. To minimize the power loss of such a clutch, only a minor slip of, for example, five revolutions per minute, may be set. Thus, the difference in rotational speed between the driving side of the clutch, which is connected to the output bevel gear pair, and the output side of the clutch may be, for example, five revolutions per minute.
An accurate control and/or regulation of the slip of the clutch requires an accurate measurement of the rotational speed difference. For this purpose, the driving rotational speed and the output rotational speed of the clutch may be measured by rotational speed sensors. However, the accuracy of the rotational speed measurements may be limited, for example, due to tolerances of the sensors. Inaccurate rotational speed measurements have a negative effect on the quality of the control and/or regulation of the slip of the clutch.
An exemplary method according to the present invention for controlling and/or regulating the slip of a clutch provides that a corrected driving rotational speed and/or a corrected output rotational speed is determined to consider errors in the measured driving rotational speeds and/or the measured output rotational speeds. The determination of the corrected driving rotational speed and/or the corrected output rotational speed is considered, with at least one driving rotational speed measured when the clutch is closed and at least one output rotational speed measured when the clutch is closed. This method may, at least partially, compensate for errors that may occur during measurement of the driving rotational speed and output rotational speed, so that the difference between the driving rotational speed and the output rotational speed may, for example, be more accurately determined. This may permit an improved quality of control and/or regulation of the slip of the clutch.
Another exemplary method according to the present invention includes the steps of: (a) closing the clutch so that the actual driving rotational speed corresponds to the actual output rotational speed; (b) measuring at least one driving rotational speed and at least one output rotational speed; and (c) determining the difference between the measured driving rotational speed and the measured output rotational speed.
Closing the clutch, as recited, for example, in step (a), means that the clutch is operated without slip. In this manner, the actual driving rotational speed corresponds to the actual output rotational speed. The measurement performed in step (b), for example, may be subject to errors. However, these errors may be detected, for example, by determining, in step (c), the difference between the measured driving rotational speed and the measured output rotational speed (which would be zero in an error-free measurement).
Still another exemplary method according to the present invention includes the additional step of: (d) determining a differential function by recalculating the difference between the measured driving rotational speed and the measured output rotational speed to other rotational speeds.
Step (d) permits the information about measurement errors obtained by steps (a) through (c) to be applied to rotational speeds, for which steps (a) through (c) have not been performed.
In this regard, the differential function may be determined in accordance with a preselected characteristics map, which may show, for example, the measurement errors in revolutions per minute as a function of rotational speed.
In addition, or as an alternative, the differential function may be determined as a function of the measured driving rotational speeds and/or the measured output rotational speeds.
In this regard, the differential function may be determined as a function of the measured driving rotational speeds as follows:
f(nse)=nse*(nse1xe2x88x92nab1)/nse1, 
in which nse is the measured driving rotational speed, nse1 is a driving rotational speed measured when the clutch is closed and nab1 is an output rotational speed measured when the clutch is closed. Such a differential function may be formulated, for example, when it is assumed that the driving differential nse1 has been measured correctly.
Yet another exemplary method according to the present invention includes the additional step of: (e) determining the corrected driving rotational speed and/or the corrected output rotational speed by adding the value of the differential function to the measured driving rotational speed and/or to the measured output rotational speed.
If the differential function is determined as a function of the measured driving rotational speeds, as described above, the corrected output rotational speed may be determined by adding the value of the differential function to the measured output rotational speed.
Still another exemplary method according to the present invention includes the additional step of: (f) forming the difference between a measured driving rotational speed and a corrected output rotational speed and/or forming the difference between a measured output rotational speed and a corrected driving rotational speed and using the difference to control and/or regulate the slip.
As described above, accurate determination of the rotational speed difference between the driving rotational speed and the output rotational speed of the clutch is essential for the quality of the control and/or regulation of the slip of the clutch. By determining this rotational speed difference according to step (f), measurement errors, which may occur during measurement of the driving rotational speed and the output rotational speed, may be at least partially compensated for, thereby producing improved results.
An exemplary device according to the present invention for controlling and/or regulating the slip of a clutch determines a corrected driving rotational speed and/or a corrected output rotational speed by considering at least one driving rotational speed measured when the clutch is closed and at least one output rotational speed measured when the clutch is closed, to consider errors in the measured driving rotational speeds and/or the measured output rotational speeds. This may permit errors in the measurement of the driving rotational speeds and/or output rotational speeds to be at least partially compensated for, so that the difference between the driving rotational speed and the output rotational speed, for example, may be more accurately determined. This may improve the quality of the control and/or regulation of the slip of the clutch.
Another exemplary device according to the present invention determines a difference between a driving rotational speed measured when the clutch is closed (i.e., the clutch is operating without slip) and an output rotational speed measured when the clutch is closed. In this manner, the actual driving rotational speed corresponds to the actual output rotational speed. However, the measurement of the driving rotational speed and the output rotational speed may be subject to errors. These errors may be detected by determining the difference between the measured driving rotational speed and the measured output rotational speed (which would be zero in the case of an error-free measurement, as described above).
Still another exemplary device according to the present invention determines a differential function by recalculating the difference between the measured driving rotational speed and the measured output rotational speed to other rotational speeds. In this manner, the information regarding measurement errors obtained through the measurements when the clutch is closed may also be applied to rotational speeds, for which no measurements have been performed with the clutch closed.
In this regard, the values of the differential function may be determined in accordance with a preselected characteristics map, which may show, for example, the measurement error in revolutions per minute as a function of rotational speed.
In addition or as an alternative, the differential function may be determined as a function of the measured driving rotational speeds and/or the measured output rotational speeds.
In this regard, the differential function may be determined as a function of the measured driving rotational speeds as follows:
f(nse)=nse*(nse1xe2x88x92nab1)/nse1, 
in which nse is the measured driving rotational speed, nse1 is a driving rotational speed measured when the clutch is closed and nab1 is an output rotational speed measured when the clutch is closed. Such a differential function may be formulated, for example, when it is assumed that the driving rotational speed nse1 has been measured correctly, as described above.
Other exemplary devices according to the present invention determine the corrected driving rotational speeds and/or the corrected output rotational speeds by adding the value of the differential function to the measured driving rotational speeds and/or to the measured output rotational speeds. If the differential function is determined as a function of the measured driving rotational speeds, as described above, the corrected output rotational speed may be determined by adding the value of the differential function to the measured output rotational speed.
Yet another device according to the present invention forms the difference between a measured driving rotational speed and a corrected output rotational speed and/or the difference between a measured output rotational speed and a corrected driving rotational speed. This difference may then be used for controlling and/or regulating the slip. As described above, the accuracy in determining the rotational speed difference between the driving rotational speed and the output rotational speed of the slipping clutch is essential to the quality of the control and/or regulation. Through the determination of this rotational speed difference, errors in the measurement of the driving rotational speed and the output rotational speed may be at least partially compensated for, so that improved results may be achieved.